1. Field of the Invention
This invention relates to a grease bath seal for use with a grease bath of a swing mechanism of a construction machine, for example, a swing mechanism on a hydraulic power shovel or excavator or a swing mechanism on a hydraulic crane.
2. Discussion of the Background
Generally speaking, construction machines like hydraulic power shovels or excavators have an excavating or other working mechanism mounted on an upper swing structure which is rotatably mounted on a vehicular base carrier. Through a swing mechanism, the upper swing structure is rotatably supported on the vehicular base carrier. The swing mechanism is largely constituted by an outer ring which is mounted on a swing frame of the upper swing structure, an inner ring which is mounted on a top frame plate on the side of the vehicular base carrier, and bearings interposed between the outer and inner rings. A swinging pinion which is rotationally driven from a hydraulic motor is meshed with a ring gear which is formed on and around the inner periphery of the inner ring. A grease bath in the form of an annular groove is provided on the side of the vehicular base carrier for pooling grease to be used as a lubricant for meshed sliding portions of the ring gear and the swinging pinion. On the inner peripheral side, the annular groove of the grease bath is bounded by a tubular wall. Upper end portions of this tubular wall have to be kept out of contact with the swing frame of the upper swing structure. Therefore, the upper end of the tubular wall in the inner side of the grease bath is usually left in an open state despite intrusion of water, mud, dirt or other pollutants through upper open portions. Intrusion of such pollutants accelerate deteriorations of grease to invite low lubricity of meshed portions of the ring gear and swinging pinion, resulting in development of rust in a worse case.
In solving the problem just mentioned, it has been known in the art to provide a seal member on a tubular wall at the inner periphery of a grease bath for the purpose of preventing intrusion of pollutants into the grease bath, as described in Japanese Laid-Open Utility Model Application S64-5961. This prior art seal member is arranged to be gripped on the tubular wall in a fixed state, with its fore end portion held in sliding contact with a swing frame.
In this connection, from the standpoint of economical use of grease, it is desirable that the grease bath has the minimum necessary capacity in volume, that is to say, it is desirable that the grease bath has a width slightly larger than the outside diameter of the swinging pinion. For this purpose, it becomes necessary to mount a seal member on a tubular wall of a larger diameter. As a result, the circumferential speed in swinging motions of the upper swing structure is increased to accelerate abrasive wear of the seal member. Therefore, the seal member prematurely loses its sealing power. In addition, when the upper swing structure and the vehicular base carrier are moved in upward and downward directions, respectively, under the influence of vibrations which are generated by a machine operation, the seal member is set apart from the frame of the upper swing structure, opening up a gap space which would permit intrusion of pollutants into the grease bath. Furthermore, at the time of replacing a seal member which no longer has a sufficient sealing power, it has been necessitated to separate the upper swing structure from the vehicular base carrier. That is to say, troublesome heavy jobs have been required for replacement of a seal member.